Sit-up exercise apparatus



FIG. 1 is a top plan view of a sit-up exercise apparatus, showing my new design;

FIG. 2 is a right side elevational view thereof;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a rear elevational view thereof;

FIG. 5 is a bottom plan view thereof; and,

FIG. 6 is a perspective view thereof. 

The ornamental design for a sit-up exercise apparatus, as shown and described. 